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754
FXUS63 KEAX 292325
AFDEAX

Area Forecast Discussion
National Weather Service Kansas City/Pleasant Hill MO
625 PM CDT Mon Apr 29 2024

.KEY MESSAGES...

- Quiet Weather Today

- Rain Showers and Thunderstorms Late Tuesday Night

- More Showers and Thunderstorms Possible Wednesday and Thursday

&&

.DISCUSSION...
-- Changed Discussion --
Issued at 425 PM CDT Mon Apr 29 2024

Surface cyclone and associated cold front has passed through the
area. A secondary mid-level trough axis is still moving across the
area but the cold front has kept most of the moisture away from the
area and overall forcing has been weak. A low-amplitude mid-level
ridge is working across the Northern High Plains, and the subsidence
ahead of this has promoted the development of a surface anticyclone
that been building across the Central Plains into the lower Missouri
River Valley. This is starting to slide underneath the secondary
trough axis and has helped to keep skies mostly clear this
afternoon. Over the Pacific Northwest a PV anomaly will support a
closed-low system but is currently progged to eject multiple vort
maxes over the next few days.

Tuesday, the first H5 vort max breaks away from the Pacific
Northwest Region and pushes the mid-level ridge axis across the
region as well as the center of the surface cyclone. Stronger
vorticity advection occurs across the Front Range and High Plains
that will promote surface cyclogenesis early Tuesday afternoon,
which will promote southerly flow at the surface into our region and
provide WAA. Currently expecting this to push temperatures up into
the lower 80s across most of the forecast area Tuesday afternoon,
and this is also representative of the inner-quartile spread amongst
NBM Members. WAA continues into the early evening hours, while a
cold front develops and propagates across the Central Plains toward
our forecast area. H5 height falls pick up in pace Tuesday evening
as the front approaches the area, increasing convergence and
enhancing overall kinematic support. MLCAPE values ahead of the
front and first H5 trough axis will be around 2000 J/kg per 12z HREF
guidance. 0-6km bulk shear along the boundary will be around 40 kts,
and currently the vector is oriented perpendicular to the boundary.
This shear environment would favor the development of a few discrete
supercells in the evening across our area mainly west of Hwy. 65.
Mid-level lapse rates will be around 7.7 to 8.0 C/km ahead of the
front which will support stronger updrafts. These updrafts in
discrete storms, especially if a supercellular mode is realized,
will present hail threat to around golf balls. However, low-level
storm-relative flow may be stronger with limited CAPE available in
the hail growth zone, which could limit hail sizes. Eventual upscale
development as the low-level jet ramps will also diminish the hail
threat once storms are no longer discrete. Depending on how robust
boundary layer mixing is throughout Tuesday afternoon, steeper
boundary layer lapse rates may support stronger cold pools initially
resulting in damaging wind gusts with stronger storms. The low-level
hodographs per RAP model soundings demonstrate a large amount of
curvature, and progged SRH values in the 0-1km layer between 150-200
m^2/s^2. Both mean wind moving storms and right moving storms could
potentially realize stronger streamwise vorticity ingest, coupled
with stronger low-level storm-relative flow that could support a few
tornadoes with supercells. However, if supercells move too far off
the boundary and get into a weak low-level shear zone, this threat
will quickly diminish and seems likely a scenario for our area.
Therefore, primarily concerned with severe hail and damaging wind
gusts with storms on Tuesday evening. The CAMs this morning and
afternoon have been favoring convection initiation between 23z and
00z from northeastern KS into southeastern Nebraska and far
northwest Missouri. These storms then move toward the southeast.
This timing seems reasonable, as the boundary layer will need a
decent amount of time to destabilize. The main uncertainty with
timing and storm propagation is when the cold front stalls over the
area after the first short-wave trough exits and a compact mid-level
ridge and H5 height rises return Wednesday Morning. There is also a
question as to how strong subsidence will be and what this will do
to precipitation Wednesday morning. This could completely clear
conditions up, but isentropic ascent across the warm-sector may
promote further shower development. CAM solutions are spread out
with how storms congeal overnight into Wednesday morning, and how
long it lasts. With respect to rainfall amounts, will be watching
closely given the flooding conditions present across much of the
area over the weekend. Current deterministic GFS/ECMWF solutions
have about 0.25 to 0.50 inches of QPF primarily north of Interstate
70, with lower amounts southward. Ensemble probabilities for at
least 0.10 inches across northern and central Missouri are around 50-
60 percent Tuesday Night into Wednesday Morning, with probabilities
for exceeding 0.50 inches less than 10 percent. Flash Flood Guidance
currently indicates one hour rainfall totals of 1.10 inches would
needed to promote flash flooding. For now, have not issued any flood
watch products related flash flood potential, as it would
likely be isolated and limited in area with a few stronger
thunderstorms. However creeks, streams, and rivers that are
already experiencing elevated flows may have their flooding
further augmented.

Wednesday, brief period of H5 height rises keeps the thermal
boundary stalled somewhere in the northern two-thirds of the
forecast area, and it is possible additional development if we see
isentropic ascent across the warm-sector Wednesday afternoon.
Perhaps more development could occur if Tuesday Night`s activity
produces a stronger outflow boundary. Current 18z CAMs show a storm
mode more consistent with WAA precipitation then truly surface based
convective parcels. Model soundings Wednesday afternoon indicate a
stronger inversion across much of the area with weaker low-level
lapse rates, as well as weaker shear as the first vorticity max and
short-wave exits the region. Therefore, environment Wednesday
afternoon is not looking favorable for organized activity, but will
need to mindful of elevated convection as mid-level lapse rates
could still be around 8.0 C/km. H5 height falls continue from the
Intermountain West into the Front Range Wednesday prompting another
round of surface cyclogenesis. Response ahead of this will promote
southerly flow and theta-e advection through Wednesday Night, which
if there is enough moisture could continue to promote WAA zone
precipitation ahead of the stalled boundary. Ensemble probabilities
for measurable precipitation into Wednesday afternoon around 40-50
percent.

Late Wednesday Night into Thursday, a stronger short-wave trough and
vort max is progged to break eastward. This will allow stronger dCVA
to deepen surface cyclone across the High Plains and Central Plains
and pushes the thermal boundary across the area. Additional showers
and thunderstorms should develop ahead of this resulting in heavier
rainfall. Ensemble probabilities heading into Thursday begin to push
above 70 percent for measurable precipitation, and 50-60 percent
probabilities for exceeding 0.50 inches of QPF. Storm mode could be
convective if there is enough destabilization of the boundary layer
ahead of the front before it begins to propagate. With these heavier
QPF amounts, concerns for Flash Flooding will increase as rainfall
rates of 1 inch in three hours will still likely be enough to
produce flash flooding. There is still a high degree of uncertainty
with how the storm mode will evolve on Thursday, and how progressive
the system as a whole will be. For now, will not issue any Flood
Watch headlines until the forecast becomes more uncertain, but
currently the soils are not in the best shape to handle as much
water that this could produce. As of any severe threat Thursday,
this will largely depend on if there is enough instability for a
convective storm mode.

In the extended forecast, there is a lot of spread in the exact
timing of trough axes across the Central CONUS but more rounds of
rain showers and thunderstorms are likely. Ensemble probabilities
are favoring additional QPF Saturday into Sunday, and then again
Monday Night into Tuesday. The timing of this may change as we
likely will be tracking a few closed-low system across portions of
Canada. It appears that high temperatures will generally be in the
mid 70s to lower 80s, but will point out the inner-quartile spread
for temperatures at most points in our forecast is quite large, as
much as 15-20 degrees of spread. This highlights the large amount of
uncertainty within the pattern, as well as difficulty in
pinpointing severe weather potential in the extended outlooks.
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&&

.AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/...
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Issued at 623 PM CDT Mon Apr 29 2024

VFR conditions are expected to remain for the duration of the
TAF period. A strengthened pressure gradient will result in
breezy conditions tomorrow afternoon with gusts as high as 30
knots. There is a potential for some scattered showers during
the morning hours and thunderstorms at the end of the forecast
period however left out of the TAFs due to uncertainty in
intensity and timing respectively.
-- End Changed Discussion --

&&

.EAX WATCHES/WARNINGS/ADVISORIES...
MO...None.
KS...None.

&&

$$

DISCUSSION...Krull
AVIATION...Collier